Vehicle High-Voltage Systems Isolation Testing

ABSTRACT

An isolation test system for a vehicle includes a communication interface, a current sensor, a plurality of impedances and a controller. The controller is programmed to electrically connect a selected one of the impedances between a traction battery of the vehicle and a low voltage subsystem of the vehicle. The connection creates a leakage path between the traction battery and the subsystem. The controller is further programmed to output a diagnostic status based on a current associated with the leakage path and a signal received via a communication interface indicative of an isolation fault between the battery and subsystem.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.14/264,342, filed Apr. 29, 2014, which claims the benefit of U.S.Provisional Application No. 61/872,709, filed Aug. 31, 2013, thedisclosures of each of which are incorporated in their entirety byreference herein.

TECHNICAL FIELD

This application relates to testing performance of hybrid and electricvehicle electrical components with regard to isolation between high andlow voltage electrical systems.

BACKGROUND

A high-voltage traction battery may be used for hybrid and electricvehicle applications. Vehicles having a traction battery may include abattery management system (BMS) having a battery electronic controlmodule (BECM) that monitors isolation between the high voltage systemand the low voltage system of the vehicle. The BECM may provide adiagnostic indicator and/or shut down various systems or subsystems ifthe isolation between the high and low voltage systems is compromised.

It may be beneficial to evaluate the performance of the isolationmonitor feature as early as possible in the development cycle of theBECM hardware and software. However, a suitable testing environment maynot be available until prototype traction battery packs or prototypevehicles are available. In addition, hardware or software changes duringvehicle development may impact isolation monitoring, and immediatevalidation and testing can be difficult to manage at the battery packand vehicle levels with limited resource availability.

SUMMARY

An isolation tester for a vehicle includes a communication interface, aplurality of impedances and a controller. The controller is programmedto electrically connect a selected one of the impedances between atraction battery of the vehicle and a subsystem of the vehicle. Theconnection creates a leakage path between the traction battery and thesubsystem. The controller is further programmed to output a diagnosticstatus based on a current associated with the leakage path and a signalfrom the communication interface.

A test system for a vehicle includes a current sensor, a plurality ofimpedances, a communication interface and a controller. The controlleris programmed respond to isolation fault feedback from the communicationinterface. The controller is further programmed to connect a selectedone of the impedances in series with the current sensor, a battery, anda subsystem of the vehicle to create a leakage path bridging anisolation barrier between a high-voltage bus of the vehicle and thesubsystem.

A method of vehicle isolation testing by a controller includeselectrically coupling a selected impedance between a traction batteryand a subsystem of a vehicle. The method further includes the controllerenabling the traction battery to energize the impedance via ahigh-voltage-interlock circuit that passes a leakage current from thebattery, through a sensor and the impedance, to the subsystem. And, themethod includes the controller outputting a diagnostic status based onthe leakage current and a signal received via a communication interfaceindicative of an isolation fault between the battery and subsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a representative vehicle having a tractionbattery and associated controller with an isolation monitor to monitorisolation between a high voltage and low voltage electrical systemaccording to various embodiments of the disclosure;

FIG. 2 is a diagram of a representative traction battery pack includinga controller and circuitry for monitoring isolation;

FIG. 3 is a diagram illustrating a representative embodiment of anisolation monitor testing device having a leakage bus connecting a highvoltage cell string to a leakage array and leakage destination or sink;and

FIG. 4 is a diagram illustrating operation of a performance tool toevaluate an isolation monitor according to embodiments of thedisclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

FIG. 1 depicts a representative vehicle having a traction battery. Whilethe representative embodiment illustrated depicts a plug-inhybrid-electric vehicle, those of ordinary skill in the art willrecognize that various embodiments may be utilized with other types ofelectric and hybrid vehicles having a traction battery. For example, thesystems and methods described herein are equally applicable to anelectric vehicle without an internal combustion engine or any otherdevice using a traction battery or battery pack and associated highvoltage electrical system electrically isolated from a low voltageelectrical system, typically 12V or 24V.

A typical plug-in hybrid-electric vehicle 2 may comprise one or moreelectric machines operable as motors 4 mechanically connected to ahybrid transmission 6. In addition, the hybrid transmission 6 ismechanically connected to an engine 8. The hybrid transmission 6 mayalso be mechanically connected to a drive shaft 10 that is mechanicallyconnected to the wheels 12. The electric motors 4 can provide propulsionand deceleration capability when the engine 8 is turned on or off. Theelectric motors 4 may also act as generators and can provide fueleconomy benefits by recovering energy that would normally be lost asheat in the friction braking system. The electric motors 4 may alsoreduce pollutant emissions since the hybrid electric vehicle 2 may beoperated in electric mode under certain conditions.

The traction battery pack 14 stores energy that can be used by theelectric motors 4. A vehicle battery pack 14 typically provides a highvoltage DC output. The battery pack or traction battery 14 iselectrically connected to a power electronics module 16. The powerelectronics module 16 is also electrically connected to the electricmotors 4 and provides the ability to bi-directionally transfer energybetween the battery pack 14 and the electric motors 4. For example, atypical traction battery 14 may provide a DC voltage while the electricmotors 4 may require a three-phase AC current to function. The powerelectronics module 16 may convert the DC voltage to a three-phase ACcurrent as required by the electric motors 4. The power electronicsmodule 16 may also convert the battery voltage to a high-voltage used indriving the electric motors 4, this conversion is accomplished by avariable-voltage DC/DC converter also referred to as a high-voltageconverter. In a regenerative mode, the power electronics module 16 willconvert the three-phase AC current from the electric motors 4 acting asgenerators to the DC voltage required by the battery pack 14. Also, in aregenerative mode, the power electronics module may convert thehigh-voltage from the electric motors 4 to a battery voltage. A highvoltage interlock may be used for both the traction battery 14 andhigh-voltage components on a high-voltage bus. The high-voltagecomponents include the electric motors 4, power electronics module 16,battery pack 14, DC/DC converter module 18 and associated componentsoperated by battery voltage or high-voltage from the variable voltageconverter. A high-voltage interlock may be used to inhibit a currentflow and high-voltage potential on the terminals of the battery pack 14.To enable the current flow and high-voltage potential on the terminalsof the battery pack 14, both an electrical and mechanical coupling ofthe high voltage interlock must be made. The high-voltage interlock isoften built into the battery and high-voltage systems, however anexternal high-voltage interlock bypass circuit may be used inconjunction with the high-voltage interlock to allow the high-voltagesystem to be powered up during testing and evaluation. Also, thehigh-voltage interlock may be used to disconnect or disable high-voltagecomponents from the traction battery pack 14 by electrically opening aconnection therebetween.

In addition to providing energy for propulsion, the battery pack 14 mayprovide energy for other vehicle electrical systems. A typical systemmay include a DC/DC converter module 18 that converts the high voltageDC output of the battery pack 14 to a low voltage DC supply that iscompatible with other vehicle loads. The low-voltage DC supply has apositive terminal and a negative terminal also referred to as a ground.The negative terminal or ground may be electrically connected to thevehicle chassis in which the chassis, a negative terminal and ground,while electrically connected, may have different electrical properties.Other high voltage loads, such as compressors and electric heaters, maybe connected directly to the high-voltage bus from the battery pack 14.In a typical vehicle, the low voltage systems are electrically connectedto a 12V battery 20 and are electrically isolated from the high voltageelectrical system. An all-electric vehicle may have a similararchitecture but without the engine 8.

The battery pack 14 may be recharged by an external power source 26. Theexternal power source 26 may provide AC or DC power to the vehicle 2 byelectrically connecting through a charge port 24. The charge port 24 maybe any type of port configured to transfer power from the external powersource 26 to the vehicle 2. The charge port 24 may be electricallyconnected to a power conversion module 22. The power conversion modulemay condition the power from the external power source 26 to provide theproper voltage and current levels to the battery pack 14. In someapplications, the external power source 26 may be configured to providethe proper voltage and current levels to the battery pack 14 and thepower conversion module 22 may not be necessary. The functions of thepower conversion module 22 may reside in the external power source 26 insome applications.

Battery packs may be constructed from a variety of chemicalformulations. Typical battery pack chemistries are lead acid,nickel-metal hydride (NIMH) or Lithium-Ion. FIG. 2 shows a typicalbattery pack 30 in a simple series configuration of N battery cells 32.Other battery packs, however, may be composed of any number ofindividual battery cells connected in series or parallel or somecombination thereof. A typical system may have one or more controllers,such as a Battery Energy Control Module (BECM) 36, that monitor andcontrol the performance of the battery pack 30. The BECM 36 may monitorseveral battery pack level characteristics such as pack current 38, packvoltage 42 and pack temperature 40. The BECM 36 may have non-volatilememory such that data may be retained when the BECM is in an offcondition. Retained data may be available upon the next key cycle.

The BECM 36 may include hardware and/or software to perform an isolationmonitor function. The isolation monitor function monitors electricalisolation of the high voltage electrical system from the low voltageelectrical system of the vehicle by detecting leakage currents. Upondetection of a leakage current that exceeds a predetermined level, theisolation monitor may set a diagnostic code and/or perform variouscontrol functions to shut down or disable one or more vehicle systems orsubsystems to reduce or prevent continued exposure of vehiclecomponents, service technicians, or occupants to high voltage. Anisolation monitor performance tool according to embodiments of thepresent disclosure may be used to evaluate the BECM 36 hardware andassociated software outside of the vehicle such that an actual vehicleor traction battery pack is not needed.

In addition to the battery pack level characteristics, there may bebattery cell level characteristics that are measured and monitored bythe BECM 36 and proper operation evaluated by an isolation monitor toolaccording to embodiments of the present disclosure. For example, theterminal voltage, current, and temperature of each cell may be measured.A battery controller 36 may include voltage monitoring circuits 34 tomeasure the voltage across the terminals of each of the N cells 32 ofthe battery pack 30. The voltage monitoring circuits 34 may be a networkof resistors and capacitors configured to provide proper scaling andfiltering of the cell voltage signals. The voltage monitoring circuits34 may also include other components for properly sampling the cellvoltages and converting the voltages to digital values for use in amicroprocessor. The voltage monitoring circuits 34 may also provideisolation so that high-voltages will not damage other circuitry with theBECM 36. An isolation monitor performance tool according to embodimentsof the present disclosure may be used to evaluate operation of thesecomponents and circuitry, as well as the ability of the BECM isolationmonitor software to detect leakage current through one or more of thesecomponents and circuitry. Performance of the BECM isolation monitorsoftware may be tested using an isolation monitor performance tool.

As generally illustrated in the representative embodiment of FIG. 3, anisolation monitor performance tool 100 may include a leakage bus 106, aleakage array 102, and a leakage destination 104. In one embodiment, theleakage destination 104 is integrated or incorporated into a batterysimulator 98 hardware interface layer. During operation, a terminal of acell 108 within the high-voltage cell string 110, which simulates amultiple cell high voltage vehicle traction battery, is selectivelyconnected to the leakage 106 bus via one or more associated sourceswitches 122 under control from the microprocessor 114. The leakagearray 102 is composed of a number of components 116, 118 to provide adesired real or complex impedance. In the illustrated embodiment, anarray of parallel resistors 116 and capacitors 118 each with differentvalues of resistance and capacitance, respectively, are selectivelyswitched by one or more level switches 112 via the microprocessor 114 toprovide the desired real or complex impedance in the leakage circuit 106or path. Other embodiments may also include inductive loads. Themicroprocessor 114 selectively activates a destination switch 120 tocomplete the leakage path or circuit. In the illustrated embodiment, onedestination is a second voltage source representing a typical vehiclelow voltage system, which may be 12V for example. Another destinationmay be connected to ground to simulate a vehicle chassis. Otherembodiments may include multiple destinations of varying voltage levels.

The isolation monitor performance tool 100 may include a harness forconnecting to a battery controller. The voltage sources 108 within thebattery simulator 98 may be connected to the battery controller in thesame manner as actual cells within the traction battery pack. The highvoltage cell string 110 may simulate the actual battery cells (FIG. 2,32). To the battery controller, the high voltage cell string 110 mayappear to be a normal battery pack when the switches are not activated.When different combinations of switches are activated, the batterycontroller may detect leakage current using an internal isolationmonitor.

The microprocessor 114 may apply various combinations of switches totest the reaction of the isolation monitor under test. Themicroprocessor 114 may monitor the response of the isolation monitorunder test over the external communication link 124. The isolationmonitor under test may send one or more diagnostic codes indicative ofisolation detection over the external communication link 124. Themicroprocessor 114 may correlate the diagnostic code to the switchsettings to ascertain if the proper behavior was taken by the isolationmonitor. The microprocessor may operate in an open loop control mode inwhich different impedances are selectively coupled and uncoupled basedon time in which correlation of the faults and impedances is performedmanually. Alternatively, the microprocessor may operate in based onclosed loop feedback in which the microprocessor selectively couples anduncouples impedances in response to signals received from the BECM. Forexample, the tester 100 may couple a very low impedance between thetraction battery and the destination (low-voltage positive, negative,ground or chassis), after which the BECM will detect the isolation faultand signal over the communication interface (CAN or Ethernet) the statusof the fault. Based on a the status signal from the BECM, the tester 100may uncouple the impedance and select a second impedance to couple totest the sensitivity of the BECM isolation testing. To improveperformance, it is desirable to have a current sensor placed in thetester 100 either on the leakage bus 106 or the leakage destination bus104. Here, the current sensor is implemented independent of theimpedances and providing a more accurate leakage current reading.

The switches may be implemented with a variety of components. Theswitches or switching elements may be implemented as relays. Themicroprocessor may energize a coil associated with the relay to move acontact. The switches may also be implemented as solid state devices,such as transistors. The microprocessor may have associated circuitry todrive a gate of a transistor device to activate the switching device.

FIG. 4 illustrates the creation of a leakage path from the top of thehigh-voltage cell string 110, through a resistor R1 150, to the 12Vsupply 158 in the low-voltage domain. This is achieved by themicroprocessor 114 closing the switches 152, 154, 156 identified withellipses. The microprocessor 114 may also provide an externalcommunication interface 124, such as Ethernet or CAN, to allow externalcontrol of the system and to provide status and feedback to externalcontrols.

Referring again to FIG. 3, the strategy implemented in themicroprocessor 114 may ensure that only one source switch 122 is closedat any time to protect against shorting cell outputs. The strategy mayalso ensure that only one destination switch 120 is closed at any timewhich, in the configuration shown in FIG. 3, prevents shorting the lowvoltage source of 12V directly to ground.

The isolation monitor performance tool 100 of the present disclosure maybe used in a laboratory testing environment during all phases of batterysystem and vehicle development. The performance tool may also beemployed by service technicians to test operation of a batteryelectronic control module (BECM) and associated circuitry duringservicing of a vehicle.

Use of the isolation monitor performance tool 100 may provide usefulinformation for battery controller design and implementation at an earlystage of vehicle development when a prototype high voltage tractionbattery or other system components may not be available. An isolationmonitor performance tool 100 of various embodiments may be integratedinto existing battery simulator devices 98, may allow introduction ofvariable leakage to a high voltage system without manual contact ofcomponents at high voltage potentials, or may allow the introduction ofcomplex impedances to a high voltage system. Other advantages of anisolation monitor evaluation tool according to embodiments of thedisclosure may include providing automated control of leakage source,variable real or complex impedance, and a selectable destination orsink. In addition, various embodiments allow the automated introductionof leakage at any point along the cell string.

The processes, methods, or algorithms disclosed herein can bedeliverable to/implemented by a processing device, controller, orcomputer, which can include any existing programmable electronic controlunit or dedicated electronic control unit. Similarly, the processes,methods, or algorithms can be stored as data and instructions executableby a controller or computer in many forms including, but not limited to,information permanently stored on non-writable storage media such as ROMdevices and information alterably stored on writeable storage media suchas floppy disks, magnetic tapes, CDs, RAM devices, and other magneticand optical media. The processes, methods, or algorithms can also beimplemented in a software executable object. Alternatively, theprocesses, methods, or algorithms can be embodied in whole or in partusing suitable hardware components, such as Application SpecificIntegrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs),state machines, controllers or other hardware components or devices, ora combination of hardware, software and firmware components.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes mayinclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. An isolation tester for a vehicle comprising: acommunication interface; a plurality of impedances; and a controllerprogrammed to electrically connect a selected one of the impedancesbetween a traction battery and subsystem of the vehicle to create aleakage path therebetween, and to output a diagnostic status based oncurrent associated with the leakage path and a signal received via thecommunication interface indicative of an isolation fault between thebattery and subsystem.
 2. The isolation tester of claim 1, wherein thecommunication interface is a controller area network (CAN) interface orEthernet.
 3. The isolation tester of claim 2, wherein the controller isfurther programmed to select a different one of the impedances inresponse to another signal received via the communication interface, todisconnect the selected one of the impedances, to connect the differentone of the impedances to the traction battery, and to output anotherdiagnostic status.
 4. The isolation tester of claim 1, whereinelectrically connecting a selected one of the impedances between atraction battery and subsystem of the vehicle includes electricallyconnecting the selected one of the impedances to fewer than all batterycells of the traction battery to create a voltage potential between thetraction battery and subsystem.
 5. The isolation tester of claim 1further comprising a current sensor disposed electrically between theselected one of the impedances and traction battery, wherein a magnitudeof the current is based on output of the sensor.
 6. The isolation testerof claim 1 further comprising a high-voltage interlock bypass circuitconfigured to pass the current when the high-voltage interlock bypasscircuit is engaged.
 7. The isolation tester of claim 1 further includinga current sensor disposed electrically in series with the tractionbattery and subsystem.
 8. The isolation tester of claim 1, wherein thesubsystem is a low-voltage positive terminal, a low-voltage ground, or achassis.
 9. A method of vehicle isolation testing comprising: by acontroller, electrically coupling a selected impedance between atraction battery and a subsystem of a vehicle; enabling the tractionbattery to energize the impedance via a high-voltage-interlock circuitthat passes a leakage current from the battery, through a sensor and theimpedance, to the subsystem; and outputting a diagnostic status based onthe leakage current and a signal received via a communication interfaceindicative of an isolation fault between the battery and subsystem. 10.The method of claim 9, wherein the subsystem is a low-voltage positiveterminal, a low-voltage ground, or a chassis.
 11. The method of claim 9,wherein the sensor is disposed electrically between the impedance andtraction battery.
 12. The method of claim 9, wherein enabling thetraction battery to energize the impedance includes electricallycoupling fewer than all cells of the traction battery to create avoltage potential between the traction battery and subsystem.
 13. Themethod of claim 9, wherein the communication interface is a controllerarea network (CAN) interface or Ethernet.
 14. A test system for avehicle comprising: a current sensor; a plurality of impedances; acommunication interface; and a controller programmed to, in response toisolation fault feedback from the communication interface, connect aselected one of the impedances in series with the current sensor, abattery, and a subsystem of the vehicle to create a leakage pathbridging an isolation barrier between a high-voltage bus of the vehicleand the subsystem.
 15. The test system of claim 14, wherein thesubsystem is a low-voltage positive terminal, a low-voltage ground, or achassis.
 16. The test system of claim 14, wherein the controller isfurther programmed to, in response to further isolation fault feedbackfrom the communication interface, select a different one of theimpedances, disconnect the selected one of the impedances, connect thedifferent one of the impedances to the battery, and output anotherdiagnostic status.
 17. The test system of claim 14, wherein thecommunication interface is a controller area network (CAN) interface orEthernet.
 18. The test system of claim 14 further comprising ahigh-voltage interlock bypass circuit configured to pass currentassociated with the leakage path when the high-voltage interlock bypasscircuit is engaged.